Simulation And Experimental Study On Seismic Response Of Isolation Structures Under Near-Fault Pulse-Type Earthquake Excitation

Earthquake motion near the fault zone has stronger destructive power than ordinary earthquake motion and is known as near-fault ground motion.The velocity pulse in near-fault ground motion is characterized by high energy,long period,and significant speed amplitude,and is therefore also called pulse-type ground motion.Depending on the formation mechanism of pulse-type ground motion,it can be divided into forward-directivity pulse-type ground motion and slip-pulse pulse-type ground motion.Using an energy-based method for identifying near-fault pulse-type ground motion,seven forward-directivity pulse-type ground motions and seven slip-pulse pulse-type ground motions were selected.The differences between them and the remaining ground motion after the velocity pulse was removed were compared in terms of acceleration,velocity,and displacement response spectra.A 5-story base-isolated frame structure was established using ETABS,and 14 near-fault pulse-type ground motions were input into the structure for simulation to verify the impact of velocity pulse on the base isolation structure.The lead-core rubber isolation bearing of the isolation layer was used as a test substructure for real-time hybrid testing to verify the authenticity of the simulation analysis.The following conclusions were obtained through analysis:(1)For forward-directivity pulse-type ground motion and the remaining ground motion after the velocity pulse was removed,the difference in the acceleration response spectrum between them shows a trend of increasing and then decreasing,while the difference in the velocity and displacement response spectra increases overall with increasing period.For slip-pulse pulse-type ground motion and the remaining ground motion after the velocity pulse was removed,the difference in the acceleration response spectrum shows a trend of increasing and then decreasing,while the difference in the velocity and displacement response spectra increases overall.By comparing the response spectra of the two types of near-fault pulse-type ground motion,it can be seen that they have rich long-period components,and the velocity pulse mainly increases the velocity response spectrum and displacement response spectrum.(2)Under the action of the two types of near-fault pulse-type ground motion and the remaining ground motion after the pulse was removed,the maximum pulse impact coefficient of the base shear,the average value of the maximum inter-story displacement angle,and the maximum acceleration of the floor for slip-pulse pulsetype ground motion are greater than those for forward-directivity pulse-type ground motion.However,the displacement of the isolation layer in forward-directivity pulsetype ground motion is greater than that in slip-pulse pulse-type ground motion,and the dynamic response of near-fault pulse-type ground motion without velocity pulse is far less than that of near-fault ground motion with velocity pulse,proving that the velocity pulse has an amplifying effect on the base shear,inter-story displacement angle,floor acceleration,and isolation layer displacement of the structure.(3)By conducting real-time hybrid testing on the lead-core rubber isolation bearing,it was found that under the action of the two types of near-fault pulse-type ground motion,the experimental displacement obtained by the test substructure is generally consistent with the simulated displacement,but the experimental displacement is larger than the simulated displacement.By comparing the experimental displacement obtained by the test substructure under the action of near-fault ground motion with and without pulse,it was found that during the pulse duration,the experimental maximum displacement under the action of near-fault ground motion with pulse is larger than that without pulse,indicating that the pulse has an amplifying effect on the displacement of the isolation layer.